The present invention relates to a method of manufacturing a golf club head, more particularly to a process of forming a face portion which can improve its durability and the rebound performance of the head.
In order to improve the rebound performance of golf club heads, it is widely employed in wood-type golf club heads in particular to decrease the thickness of the face portion. Such thinning of the face portion decreases the fatigue strength against repetition of impulsive force at the time of hitting a ball. Therefore, as a best suited material having an excellent fatigue strength, beta titanium alloys get a lot of attention.
In general, beta titanium alloys are not bad in workability in cold work. However, in case of a face plate having elaborate geometry, hot forging at over the solid solution temperature and subsequent quenching by water-cooling are usually employed to make the face plate for the working efficiency and accuracy.
It is believed in the art that if heating time of beta titanium alloy is increased, coarsening of beta phase is caused and thereby the strength and toughness are decreased. For this reason, therefore, quenching is employed after the hot forging.
With respect to some of beta titanium alloys, however, the inventor found that fatigue strength is remarkably improved, contrary to expectation, by slow cooling the alloy after hot forging, and thereby the durability of the face plate is remarkably improved because the improvement in the fatigue strength advantageously affects the durability rather than improvement in the tensile strength.